Organosilazane polymers decompose at elevated temperatures to form ceramic materials of silicon nitride, silicon carbide, and mixtures thereof. These ceramic materials are of considerable commercial interest because of their desirable properties at elevated temperatures. Problems associated with the use of organosilazane polymers as ceramic precursors include depolymerization during pyrolysis which results in low ceramic yields and the production of volatile reaction products. Methods for inhibiting such depolymerization and increasing ceramic yields are desirable to those in the ceramic field.
U.S. Pat. No. 4,482,669 discloses an organosilazane polymer which is useful for making Si.sub.3 N.sub.4 /SiC. ceramics. The polymer comprises a plurality of cyclic and/or linear precursor residues linked together by Si.sub.2 N.sub.2 bridges. The polymer is made by reacting an organodihalosilane with ammonia to form an ammonolysis product, and treating the ammonolysis product with a basic catalyst capable of deprotonating an NH group that is adjacent to an SiH group. The polymer is preferably further treated with an electrophilic reagent.
U.S. Pat. No. 4,543,344 discloses a process for preparing R.sub.3 SiNH-containing hydrosilazane polymer by contacting and reacting trichlorosilane with a disilazane (R.sub.3 Si).sub.2 NH where R is vinyl, hydrogen, phenyl, or alkyl radicals containing 1 to 3 carbon atoms. U.S. Pat. No. 4,482,689 discloses a process for preparing R.sub.3 'SiNH-containing metallosilazane polymer containing boron, titanium, or phosphorous by contacting and reacting chlorine-containing disilanes and certain reactive metal halides with [R.sub.3 'Si].sub.2 NH where R' is vinyl, hydrogen, or alkyl radical of 1-3 carbon atoms, or phenyl.
U.S. Pat. No. 3,853,567 discloses production of shaped articles such as a fiber of homogeneous mixtures of silicon carbide and nitride. The articles are produced by pyrolyzing at about 200.degree. C. to 800.degree. C. a silazane to produce a fusible carbosilazane resin, forming the resin into fiber and heating the fiber in an inert atmosphere to about 800.degree. C. to 2,000.degree. C. U.S. Pat. No. 3,892,583 discloses production of shaped articles of silicon carbide and silicon nitride. A melt or solution of a silazane is formed into a shaped article by molding or melt or dry extrusion and is thereafter heated in an inert atmosphere to about 800.degree. C. to 2000.degree. C. to decompose the silazane into a homogeneous mixture of silicon carbide and silicon nitride. The silazane is produced by reacting ammonia with a halogenosilane and, if effected in solution, after removal of by-product ammonia chloride and optionally concentrating, the solution is directly employed for shaping.
Penn et al., NASA Technical Memorandum-86505, (March, 1985) discloses preparation of silicon carbide-silicon nitride fibers (SiC-Si.sub.3 N.sub.4) by the pyrolysis of polycarbosilazane precursors. Penn et al., Journal of Applied Polymer Science, 27:3751 (1982) discloses preparation of silicon carbide-silicon nitride fibers (Si.sub.x N.sub.y C.sub.z) by the pyrolysis of polycarbosilazanes prepared from tris(N-methylamino)methylsilane.